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From: "Spehro Pefhany"
Subject: Re: Digital Meter Scaling Question
Newsgroups: sci.electronics.design
References: <20021007093614.03599.00001583@mb-fk.aol.com>
Organization: Rather
User-Agent: tin/pre-1.4-19990216 ("Styrofoam") (UNIX) (Linux/2.2.14 (i586))
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Date: Mon, 07 Oct 2002 18:42:26 GMT
NNTP-Posting-Host: 24.112.78.0
NNTP-Posting-Date: Mon, 07 Oct 2002 14:42:26 EDT
The renowned Ed Edmondson wrote:
> I have a Datel panel meter rated at 2 volts full scale and I am measuring a
> voltage in the 200 mV full scale range. Is there anyway to us an op amp to
> increase the measured voltage to operate this meter and obtain better
> resolution? The meter works OK on the 2 volt range but all the readings are
> 0.XXX volts instead of X.XXX volts.
Typically the reference is just dropped to 100mV from 1 volt, and a couple
changes are made to the auto-zero and integrating components and presto,
100uV resolution with less than a count of noise and no appreciable zero
drift.
To use an op amp with a 10:1 gain is possible, easy even, but you'll have
to pick the op-amp carefully (Vos and TCVos and maybe Ib) and take into
account the common mode range of the op-amp. Easiest to use (not cheapest)
would be a rail-to-rail chopper op amp, which would be much better than
you need.
Best regards,
Spehro Pefhany
--
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